I have a 1966 F250 and have been driving it for almost 2 years now, although rarely at night. This morning before daylight I drove to work(about 45 minutes away). I was using my high beams and suddenly they started turning off and then back on about every second or two. I had been driving for around 20 minutes when this started and had been using high beams for around 15 minutes(although I was dimming them occasionally when meeting another vehicle). The amount of time the lights stayed off in between them turning on again seemed to be increasing as time went on and I pulled off to the side of the road. I examined around the dimmer switch to see if the connector was loose and it wasn't. I examined near the headlights to make sure no wires were loose as well. I turned on my low beams for the rest of the drive with no further issues(other than nearly hitting a deer that was standing in the road because I didnt see it until I was too close to stop).

After work I drove home(in the daylight) and went to the parts store and bought a new dimmer switch since that seemed like the most likely thing to be wrong. After dark I went out and drove it for a while with the high beams and sure enough it happened again after about 15 minutes of use. I'm not sure what the issue is but it seems to be related to the high beams. Ive driven it quite a bit with the low beams at night around town and never had this issue. I believe something might be overheating and tripping the relay? The only other idea I have is it could be a grounding issue but I find it unlikely since it seems to always happen after being used for a while and only happens to the high beams.

 

Replace the dimmer switch. This is a common problem with this switch that was used from the 1960's into the 1990's.

When driving on low beams and you step on it for high beams, the headlamps go out.

Edit: You replaced the switch, but most auto parts store parts in today's world are made in China crap. So the new switch may be defective.

 

They just randomly go out without pressing the switch when high beams are already on usually after the truck has been ran for 15-20 minutes. You might be right, but I find it unlikely that its the switch seeing that I already replaced it and it consistently does it after about 20 minutes of running high beams. I'm pretty certain its an electrical issue of some sort possibly something getting overloaded?

 

Headlights don't use fuses, the switch itself has an integral circuit breaker. That's what you're experiencing. Headlight wiring runs a long route, what happens is the ground cables and connections, junction blocks etc become corroded and make for high resistance (heat) and trip the breaker intermittently.

Now you'll hear that headlight relays are the solution, and they do work, but the actual defect is that the grounding to block & frame & firewall need attention by now, if they are original they should be replaced. Every single electrical connector in these old cars and trucks is corroded by now. It doesn't take much, even an invisible, paper thin layer of corrosion at a connection is enough to cause trouble. The headlights & turn signals ground through the radiator support and frame. Everything has to be low resistance all the way back to the switch. Relays will take the load off the switch, but it still needs to be fixed.

You can use your voltmeter to track down the bad grounds or connections by using the "voltage drop test". It's important to fix for obvious reason and because it will ruin the switch (heat).

 

My '65 F100 did this, after switching to high beams, the headlights would begin to flash off and on...and this occurred in 1967 with less than 20,000 miles "on the clock."

I replaced the switch, owned it till 11/2009, never had the problem again.

 

Hi Bill what is the switch part number please and does anyone have any genuine ones in stock

 

COTZ-13A024-A .. Dimmer Switch (Motorcraft SW-263) / Obsolete

CROSSROAD FORD TRUCKS in Springfield IL has 2 = 217-391-1984.

LINCOLN-MERCURY OLD PARTS STORE in Clearwater FL has 3 = 727-445-7551.

CARPENTER NOS OBSOLETE PARTS in Concord NC has 15 = 704-786-8139. (These may be repro's).

MCDONALD OBSOLETE PARTS in Rockport IN has 54 = 812-359-4965.

 

Generally, this only happens when running halogen or other upgrade beams that draw more amperage, causing the headlamp circuit breaker to trip. There are wiring kits available that utilize relays to power the headlamps, bypassing the poor factory wiring design.

 

Is it the same issue if they just turn off after a while be it high or low beam? My low beams will work fine for a while, but then they go out randomly. I am now in the habit of watching the lights of any vehicle in front ot me just to have something to track on when they do go out and it's real fun when no one is there. Usually either flicking the power on the headlight switch or hitting the brights will bring them back, but they will sometimes go back out. Both the headlight and bright switches have been replaced, but I'm not above getting another one. My next thought was wiring, which is what I seem to see the consensus is here. Am I correct?

 

No, apparently this was an issue even with fairly new trucks "back in the day". They (OEMs) did cheap out on the vehicle wiring harness gauge and ground path.

I've ran halogen lamps with a stock 30 amp generator equipped slick with no problems for almost 20 years. Pencil out the current draw of halogen lamps versus tungsten they are well within design limits for the wiring and switches. Everything has to be clean and tight though.

What halogen lamps won't do is provide brighter light, if the current/voltage is being starved. Classic mistake, I know because I made it myself. It's important for the OP to understand that relays will take the load off the headlight switch, but the underlying fault is what really needs remedied. Poor grounds and connections also starve the ignition, starter, charging, and accessories. This is always a problem in cars and trucks after 50 or 60 years, but it's of course most noticeable with the lighting.

The headlights switched via relays will REALLY work well when or if they first get the juice they need. The goal is to reduce voltage drop to the bare minimum, even just a tenth or two of a volt makes a big difference in light output.

 

People want crazy prices for them now. I tried to find one for my 1987 F-150 before. So I just got one at NAPA. Ford retail use to be 15 or 16 bucks. But I guess it is supply and demand.

 

Read "Whiter whites and brighter brights" in the tech article section here. It is a really old article and since it was written you can buy easy to install relay wiring harnesses that are not expensive and are plug and play. Fixing grounds, replacing the dimmer switch and checking to see that the harness is plugged-in tight on the switch are all good ideas. The relay deal is better.

 

No it is not better, because without remedying the underlying electrical defects, the actual cause of the problem, it's simply wiring around them with a kluge. The circuit breaker cycling is a symptom not a cause.


YES, the headlights will be brighter when relays are installed no argument, BUT, the ignition, starting, charging, and accessories are still be starved for current. Trust Me. These old cars and trucks always have electrical problems due to corrosion. Always. Some of those wiring connections, bullet connectors, block pin connectors, grounds, haven't been touched in over 50 years. Gee, I wonder what it could be?? It's just the headlights blinking off at night tend to grab people's attention!

If the OP gets the voltage drop into spec, he may even decide relays aren't even really necessary. They will work even better, with adequate current and voltage if they are installed.

 

I disagree. You will have a voltage drop to the headlights using stock wiring simply because of the factory routing.
There’s a reason modern cars use relays. Adding relays and a more direct headlight harness is an improvement over an obsolete wiring design.

 

It's minimal if the grounds, cables, connections, terminals, etc, etc, are in good condition. When voltage drop is within spec - surprise! The switch no longer heats up, and the breaker won't trip. Every old car and truck WILL have electrical problems unless steps are taken to improve grounds and connections. I know this, because I've driven my 55 year old slick for almost 20 years. I had all the problems everybody describes when I got it, and after cleaning everything up and replacing cables, they worked fine. With Halogens. Using a Generator charging system.


Nobody claims headlight relays aren't an improvement, just pointing out what's really going on. Fix the underlying problem first/before/in addition to adding headlight relays. Blinking headlights just tells us the entire electrical system is buggered, guaranteed.